A pressurized EVA glove resists every finger-joint flex because the suit's internal gas pressure pushes the fabric back toward its inflated, straight shape. The simplified biomechanical model used here is:
T_resist = k · P · sin(θ)
k — glove fabric/joint stiffness coefficient
P — suit pressure differential (kPa)
θ — joint bend angle (max at mid-flex, θ ≈ 70°)
Higher suit pressure or a more sharply bent joint both increase the torque the astronaut's hand has to fight just to close the glove, before any torque is left over to turn the valve. The net torque delivered to the valve each squeeze is:
T_net = (effort/100) · T_MVC · capacity(fatigue) − T_resist
capacity(fatigue) = 1 − 0.8 · (fatigue/100)
Fatigue accumulates while the muscles are actively squeezing, following the shape of Rohmert's classic %MVC–endurance curve: high-effort grips burn out disproportionately fast (fatigue gain scales with effort² per squeeze), and the hand slowly recovers whenever it isn't actively gripping.
- Suit pressure — sets how hard the glove itself pushes back on every joint flex.
- Grip effort — how much of the astronaut's maximum voluntary contraction is committed to each squeeze; higher effort turns the valve faster but fatigues the hand faster too.
- Task cadence — how often a squeeze is attempted; a faster cadence leaves less time to recover between grips. Switch to manual mode to time your own squeezes against the recovery curve.
- When accumulated fatigue drops available capacity below what the glove resistance demands, net torque goes negative — the squeeze fails and the valve does not turn.
Note on this model: the original 3D version of this simulator applied an extra ×100 scale error to T_resist, which pushed the resistance torque at the suit's own realistic default pressure (29.6 kPa / 4.3 psi, the actual ISS/shuttle EVA suit pressure) to 7.23 N·m — above the 6.0 N·m maximum possible drive torque even at 100% effort and zero fatigue. That made the task mathematically unwinnable at its own suggested defaults, for any slider combination. This 2D version keeps the same linear-in-pressure, sin(θ) shape but recalibrates the stiffness constant so T_resist spans roughly 1.4–5.1 N·m across the full 15–55 kPa range — pressure still meaningfully raises the difficulty, but the task stays winnable at low-to-mid effort near the realistic default and becomes a real (not impossible) challenge only near maximum suit pressure.